We are studying details of the mechanism for synthesis of the RNA primer for synthesis of nascent DNA. The significance of deoxyuridylate misincorporation into (and removal from) DNA for the effects of methotrexate are being investigated. A protein covalently associated with parvoviral replicative form DNA, which was described in this laboratory, is being characterized. The mechanism of DNA replication in parvovirus H-1, which appears to be continuous, is being studied in vivo and in vitro.